This invention relates generally to a wire dot printer, and more particularly, to a printing head for use with a wire dot printer.
Enhancements are constantly sought in printing quality and processing speed of wire dot printers especially since wire dot printers are commonly used with computer terminal equipment for forming character patterns or the like on a recording medium. Conventional printing heads are disclosed in U.S. Pat. No. 4,669,898 and Japanese Patent Laid-Open Publication No. 29681/1983.
As shown in FIG. 5, a conventional printing head 100 includes a plurality of printing levers and a corresponding plurality of guide holes 108. Printing levers a are radially disposed and directed toward a projection of guide holes 108, which are arrayed in two lines at a nose top end of printing head 100. The inner ends of printing levers a are aligned so as to form an elliptical path 112. A corresponding plurality of printing wires b extend on an incline from the inner ends of printing levers a (hereinafter referred to as joining points c). Each printing wire b has a printing terminal end at a guide hole 108. A projected distance l between joining point c and printing terminal end d of each printing wire b is reduced in length as much as possible. Deflections of printing wire b are thereby minimized, resulting in a reduction in friction between printing wires b and the walls of guide holes 108. Furthermore, by reducing the length of printing wires b as much as possible the inertia of each printing wire b decreases resulting in an increase in printing process speed.
When the inner ends of printing levers a are concentrated at the center of printing head 100 so as to form elliptical path 112, adjacent printing wires b are disposed in such close proximity to one another that they may contact each other, especially in the end regions exemplified by a circle 114. More particularly, the inner ends of printing levers a along the region defined by the relatively large elliptical curve 112 are in such close proximity to one another that a sufficient number of printing wires b to provide a high level of printing quality is impossible.
To avoid printing wires b from contacting each other, tolerances associated with the processing and assembling of parts forming printing head 100 are quite small, that is, there must be a significant increase in the accuracy of processing and assembling the parts forming printing head 100. Production costs associated with printing head 100 undesirably and unnecessarily can significantly increase.
Accordingly, it is desirable to provide a printing head for a wire dot printer which produces printed matter of high quality. An increase in printing speed without increasing the need for producing and assembling the parts of the printing head more accurately is also desirable.